1. Field of the Invention
This invention relates to catalysts, catalyst systems and their use in olefin polymerization. The invention more particularly relates to substituted hafnium metallocene-type catalyst compounds, catalyst systems thereof, their use in a polymerizing process, their polymer products and articles thereof.
2. Description of the Related Art
The use of bulky ligand transition metal catalyst compounds in polymerization processes to produce a diverse array of new polymers for use in a wide variety of applications and products is well known in the art. Typical bulky ligand transition metal compounds, known as metallocene-type compounds, are generally described as containing one or more ligands capable of xcex7-5 bonding to the transition metal atom, usually, cyclopentadienyl derived ligands or moieties, in combination with a transition metal selected from Group 4, 5 or 6 or from the lanthanide and actinide series of the Periodic Table of Elements. Predominantly in the literature the transition metal is from Group 4, particularly either titanium, zirconium or hafnium, and the cyclopentadienyl derived ligand or moiety is substituted with various radicals, typically alkyl radicals, or two or more cyclopentadienyl ligands are joined by a structural bridge, usually an organic or inorganic group, typically, a carbon or silicon atom containing group.
Other forms of these metallocene-type catalyst compounds contain a cyclopentadienyl derived ligand or moiety and a heteroatom containing group bonded to a transition metal, typically titanium, where the cyclopentadienyl ligand or moiety and the heteroatom containing group are joined by a structural bridge, usually a silicon atom containing group. These and other metallocene-type catalyst compounds in combination with an activator form metallocene-type catalyst systems capable of polymerizing various olefin(s), alone or in combination with other olefin(s). The development of these and other metallocene-type catalyst compounds and catalyst systems are described in U.S. Pat. Nos. 5,017,714, 5,055,438, 5,096, 867, 5,198,401, 5,229,478, 5,264,405, 5,278,119, 5,324,800, 5,384,299, 5,408,017, 5,491,207 and 5,621,126 all of which are herein fully incorporated by reference.
It is well known in the art, although not fully understood, that where the transition metal of these metallocene-type catalyst compounds is hafnium, often referred to as a xe2x80x9chafnocenexe2x80x9d, hafnocene catalyst systems generally, among other characteristics, perform relatively poorly in comparison to their titanium, especially their zirconium equivalents, often referred to as xe2x80x9czirconocenesxe2x80x9d. Although hafnocenes will typically polymerize polymers having higher molecular weights than their zirconocene equivalents under similar polymerization conditions, their overall poor activity make them inferior polymerization catalysts. European patent EP 0 284 707 B1 granted Aug. 30, 1995, which is fully incorporated herein by reference, describes a process for polymerizing olefins using a catalyst system, in liquid form, containing a chiral, sterorigid bridged hafnium metallocene catalyst compound and an aluminum compound.
Thus, it would be highly advantageous to have a hafnium metallocene-type catalyst system capable of polymerizing olefin(s) with improved catalyst performance.
This invention relates to a substituted bulky ligand hafnium transition metal metallocene-type catalyst compound and a catalyst system thereof. The invention also relates to a polymerization process for polymerizing one or more olefin(s) utilizing the substituted bulky ligand hafnium transition metal metallocene-type catalyst compound.
In one embodiment, the invention provides for a catalyst system of a bulky ligand hafnium metallocene-type compound where at least one bulky ligand is substituted with a substituent having at least 3 or more non-hydrogen atoms, and an activator. Preferably, the bulky ligand is substituted with a subtituent having at least 3 or more carbon atoms or silicon atoms or combinations thereof.
In a preferred embodiment, the invention provides for an activated catalyst system of a bulky ligand hafnium metallocene-type catalyst complex where the bulky ligand is capable of xcex7-5 bonding to the hafnium transition metal and is substituted with an alkyl substituent having 3 or more carbon atoms, preferably where the alkyl substituent has 3 to 5 carbon atoms, more preferably the alkyl substituent is a linear alkyl. In one preferred embodiment, the alkyl substituent is at least one n-butyl group, most preferably at least one n-propyl group, substituted to at least one of the bulky ligands.
In yet another embodiment, the invention is directed to a process for polymerizing, preferably in a continuous process, one or more monomer(s) in the presence of the catalyst system or activated catalyst complex described above.
In one preferred embodiment, the above process of the invention is a continuous slurry or gas phase polymerization process. In another embodiment, the invention is directed to a polymer product produced using the hafnocene catalyst systems or complexes described above, wherein the polymer product contains less than 5 ppm hafnium, preferably less than 2 ppm hafnium.